> The problem with having standards for this kind of thing is that different units have different needs for communication and different levels of being smart.
There really is nothing complicated there. I have some background in lift (elevator) systems, and they have similar requirements. Modern lift systems use variable frequency drives for smooth start/stop, and they came up with compatible protocols that allow users to mix-and-match controllers.
In the end, there just needs to be a simple protocol to command the motor to run at a certain speed. It can be CAN-based, it can be based on RS-485, etc. For additional smarts, throw in readings from the sensors inside the AC units (pressure, coils temperatures).
Then the control units can be made by third parties. They can do all kinds of prediction-based logic, complicated PID controllers, whatever.
> Some of these systems attempt to be "smart" and just use the 24V C/W/Y1/Y2 etc protocol as a "standards compliant fallback". You don't necessarily lose ALL of the smarts
You actually do with TRANE units. They become completely dumb, not even 2-stage emulation.
> The closest thing I can think of to a standard, and the way it is solved in larger buildings, is through something called BACnet.
I have BACnet at home, for wired temperature/humidity sensors, the same RS-485 network is also used for Somfy shades ( https://github.com/Cyberax/py-somfy-sdn ). BACnet is a low-level system, and it needs higher-level profiles. But yes, exposing the motors and the sensors inside the AC units over BACnet would be a great start.
There really is nothing complicated there. I have some background in lift (elevator) systems, and they have similar requirements. Modern lift systems use variable frequency drives for smooth start/stop, and they came up with compatible protocols that allow users to mix-and-match controllers.
In the end, there just needs to be a simple protocol to command the motor to run at a certain speed. It can be CAN-based, it can be based on RS-485, etc. For additional smarts, throw in readings from the sensors inside the AC units (pressure, coils temperatures).
Then the control units can be made by third parties. They can do all kinds of prediction-based logic, complicated PID controllers, whatever.
> Some of these systems attempt to be "smart" and just use the 24V C/W/Y1/Y2 etc protocol as a "standards compliant fallback". You don't necessarily lose ALL of the smarts
You actually do with TRANE units. They become completely dumb, not even 2-stage emulation.
> The closest thing I can think of to a standard, and the way it is solved in larger buildings, is through something called BACnet.
I have BACnet at home, for wired temperature/humidity sensors, the same RS-485 network is also used for Somfy shades ( https://github.com/Cyberax/py-somfy-sdn ). BACnet is a low-level system, and it needs higher-level profiles. But yes, exposing the motors and the sensors inside the AC units over BACnet would be a great start.